Stoker control system



F. E. LANGE oct. 1o, 1939.

sToxER CONTROL 'sys'.vlalvl` Filed F'eb. VlO, 1939 ,'nuentor Fre-dl@ Patented Oct. 10, 1939v UNITED STATES PATENT OFFICE STOKER CONTROL SYfSTEM Frederick E.'Lange, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a corporation of Delaware Application February 1o, 1939, serial No. 255,633

14 Claims. (Cl. 11G-1) My invention relates to' an improved control system for solid fuel burning combustion systems wherein the solid fuel can be ignited in response to a thermostat or equivalent instruments. v

One of the objects of my invention is'to ob-` viate the need of fire-maintaining control devices in solid fuel'tred combustion apparatus and especially to dispense entirely with calibrated l0 combustion responsive switch devices. My invention comprehends automatically .initiating combustion in a combustion chamber in response to a thermostat if the re is out at the time the thermostat demands heat. If 'combustion val- 15 ready exists when'the lthermostat calls for heat the combustion initiating apparatus is not operated, the operation of the said apparatus being governed by a controll arrangement not employing calibrated 'combustion responsive switches. Such switches have been used in the past for re maintaining purposes but their use has entailed serious difliculties on account of the high temperatures to which they are subjected and the chemical action of gases of combustion on them tending to impair their adjustments and shorten their span of life. ,My invention avoids the use of calibrated combustion responsive switches but still provides for a fully automatic system wherein if the fire is out -when the thermostat demands heat it is automatically started.

Another object of my invention is to provide an automatic system for igniting solid fuel in a ncombustion chamber in response to a thermostat whenever .there is no increase in temperature in the combustion chamber after a thermostatic demand for heat indicating that the re is substantially out.

Another object is to provide an automatic system having means for automatically initiating combustion of solid fuel in a combustion cham-.-

ber, the combustion initiating means being controlledbyl a device 4responsive to temperature change in the combustion chamber whereby the combustion initiating means are made effective in the absence o f a temperature increase after a thermostatic demand for heat.-

Another object is the provision of a'soiid fuel igniting device controlled by a slip friction combustion responsive switch and a thermostat arranged to make the igniting device effective only" 'in the retort and automatically controlling the wherein upon a demand for heat, there is a time delay, and in the absence of a temperature rise,

'piration of the period, fueligniting means are rendered operative depending upon whether or not there has been a temperature increasein the combustion space. The other objects and advantages of the invention will become .apparent from the accompanying drawing and description. The single `figure of'the drawing represents 15 diagrammatically a stoker red furnace system having my invention embodied therein.

Referring to the drawing I have representedy at I0 a portion of the stoker red furnace which may be of a conventional type having a retort I I therein of well known form familiar yto those skilled in the art. Surrounding the retort is a plate I2 forming a fuel supporting surface for solid fuel I3. The upper part ofthe side walls of the retort II has suitable openingstherein to permit the passage of air therethrough for purposes of combustion. 'Ihe furnace I0 has a casing or jacket I4 enclosing it in a manner well known in the art, the upper .part of' the casing forming a lbonnet for the furnace. A stack 22 serves to carry -olf the products of combustion within the combustion chamber. Numeral 20 designates a distributing duct for conveying warm air from within the casing I4 to spaces to be heated and the air may be returned to the casing through a return air duct 2l. Numeral I5 'designates an automatic stoker driven by an electric motor I6, the stoker being' of a known type and having a hopper I1 into which the solid fuel is loaded. Ihe stoker I5 supplies solid. fuel to the retort II through a passage or conduity IB within which is located a screw conveyor or va conveyor of other-suitable type.- The motor I6 driving the stoker also drives a blower for providing forced draft for. the furnace the draft airbeing forced through a supply duct I9 communicating with the space around retort II and underneath the grate I2.

My invention is primarily concerned with means for automatically igniting the solid fuel igniting means. For the purpose of igniting solid fuel I provide an igniting unit generally designated at 23 comprising a gas burner nozzle 2l and.' an ,element 25 projecting through a side wall of. l.

the retort, the arrangement of the burner nozzle 24 and element 25 being such as to form a Bunsen burner which may be called a gas torch. The element 25 is so arranged that air forced into the space around retort and the flame from the burner nozzle 24 are projected through the element 25 and directed so as to impinge directly on the solid fuel within the retort. 'I'he burner nozzle 24 is supplied with gaseous fuel through a conduit 26 and in the conduit 26 is interposed a magnetic type gas control valve 21. Adjacent the extremity of the burner nozzle 24 is a constantly burning pilot burner 28 which is continuously supplied with fuel through a tube 29 connected to the conduit 26 ahead of the control valve 21. Adjacent the pilot burner 28 is a safety pilot generally designated at 3| which takes the form of a bimetal element 32 which is normally heated and flexed into engagement with a fixed electrical contact 33. Whenever gas is admitted to the burner nozzle 24 it is ignited by the llame of the pilot burner 28.

My system is primarily controlled by a space thermostat 35 responsive to the temperature of air or other medium the temperature of which is affected by heat generated in the furnace I0. The thermostat 35 is of a known type comprising a bimetal element 36 arranged to actuate two flexible switch blades 31 and 38, the blade 31 cooperating with fixed electrical contact 39 and the blade 38 cooperating with a xed electrical contact 40. 'Ihe blades 31 and 38 engage their respective contacts sequentially, the blade 31 engaging contact 39 at a predetermined temperature which may be '72 for' example and the blade 38 engaging contact 40 at a predetermined lower temperature which may be one or two degrees lower for example. Thermostat 35 controls a relay generally designated at 42 comprising a coil winding 43 which cooperates with an armature arranged to move switch blades 44, 45, and 46 to the left into engagement with the respective fixed contacts 41, 48, and 49 when the winding 43 is energized.

Further control is provided by temperature responsive switches 50 and 55. 'I'he switch 50 is a slip friction type stack switch of a known type patent, the operative engagement between the thermostatic element 53 and the mercury switch 5| is frictional and is of such a nature that upon a rise in temperature of a certain number of degrees the switch 5| is actuated in one direction and upon a fall in temperature of a certain number of degrees the switch 5| is actuated in the opposite direction, the actuations of the switch occurring upon changes in temperature and not being dependent upon the magnitude of the temperature for the switch operations to be brought about. The switch 5| in my particular system is moved to open position upon a rise of temperature of several degrees in the stack 22. The switch 55 is a known type of instrument comprising a mercury switch 56 actuable by a helical thermostatic element 51 responsive to the temperature of the air within a furnace bonnet. Switch 56 is normally-closed forming a high limit switch only opening in response to a predetermined relativiely high temperature within the furnace bonne Cooperating in' the control of my systemis a timing unit 59. 'I'his unit is a known type of timer and its details form no particular part of my invention. It comprises two bimetal elements 68 and 6| attached together at their ends as shown and disposed so as to flex oppositely in response to heat. Due to this arrangement ambient temperatures which affect each element equally are compensated for. The element 6| carries the contact 62 cooperable with a fixed electrical contact 63. Adjacent the element 6| is an electrical heating resistance 64. Upon energization of the heater 64, after a predetermined time which may be 30 seconds or a minute, for example, contact 62 will be brought into engagement with contact 63 completing an electrical circuit through the timer. The manner of cooperation of the timing unit in the system will be brought out in the description of operation following.

Power is supplied to my system from line wires 65 and 66 which may be. connected to a suitable source of external power. Low voltage power for the various control instruments and devices is provided by a step-down transformer 61 having a primary winding 68 and a secondary winding 1| the primary winding having a greater number of turns than the secondary winding. The primary winding is connected to the line conductors 65 and 66 by wires 69 and 10.

In operation, the thermostat 35 automatically controls the heating apparatus so as to supply heat whenever there is a demand made by the thermostat. The supply of fuel to the combustion chamber is intermittent as determined by the thermostat and these calls for heat may be of long duration and closely spaced or of short duration and more widely spaced depending upon the heating load imposed upon the equipment. When the load is relatively light and the periods during which the thermostat is not demanding heat are relatively long the fire in the combustion chamber may go out entirely or may recede to such a low condition that it would not recover upon the addition of fresh fuel thereto. Assuming that the fire has gone out or has practically gone out and the thermostat 35 indicates a demand for heat, blades 31 and 38 will bein engagement with their respective fixed contacts and a circuit for relay 42 will be established as follows: from thermostat `blade 31 to contact 39, Wire 13, secondary winding 1|, wire 14, wire 15, safety pilot 3|, wire 16, switch 56, wire 11, coil 43, wire 18, contact 40, and thermostat blade 38 back to blade 31. As soon as this circuit is established, relay 42 is energized causing blades 44, 45, and 46 to move to the left into engagement with xed contacts 41, 48, and 49. Engagement of blade 44 with contact 41 establishes a maintaining circuit for coil 43 as follows: from blade 31 to contact 39, wire 13, secondary 1|, wire 14, wire 15, safety pilot 3|, wire 16, switch 56, wire 11, coil 43, wire 19, blade 44, contact 41, Wire 80, and thermostatic element 36 back to blade 31. As will be observed, this latter circuit is independent of blade 38 of the thermostat so that after having been energized relay 42 will not be deenergized until the temperature rises to a value of 72 at which blade 31 engaged contact 39. Thus the thermostat 35 has a fixed operating differential and operates in a manner whereby chattering of the relay due to insecurely made contacts is eliminated.

As soon as blades 45 and 46 engage their respective contacts 48 and 49, circuits are established for energizing the heater 64 and the motor I6 driving the Stoker and blower, the circuit for 75 the heater 64 being as follows: from secondary winding 1| through wire 14, wire 8|, wire 82,

heater 64, Wire 83, contact'48, switch blade ||5,v

wire 84, wire 85, switch 5|, and wire 86 back to 5 secondary winding 1|.

be closed because the combustion chamber is cold. The circuit for the stoker and blower motor I6 is as follo'ws: from the line conductor 66 through wire 81, blade46, contact 49, wire 88, motor I6,

10 and wire 89 back to line conductor 65.

Upon completion of the circuits just describedl contacts 62 and 63-will be brought together completing a circuit,l for energizing and opening the valve 21. This circuit is as follows: from secondary 1| through wire 14, wire 8|, wire 90, timer 25 unit 59, wire 9|, valve 21, wire 92, wire 85, switch 5|, and wire 86 back to secondary 1|. i The opening ofA valve 21 admits fuel to the burner nozzle 24 where it is ignited by pilot burner 28 and the flame from nozzle 24 and air forced into the 30 space around the retort are directed through the element 25 in the manner of a torch, the flame impinging directly upon the solid fuel in the retort and serving to ignite it. there has been a rise in temperature within the 35 combustion cha'mber indicating that combustion has been established the element 53 will open the mercury switch 5| deenergizing the valve 21 and cuttingy off the supply of fuel to the burner 24.

Operation of the stoker and the draft blower will of course continue as long as the relay 42 is energized.' Whenever -the thermostat 35 becomes satisfied blower 31 will separate from contact 39 deenergizing relay 42 and discontinuing operation of the motor I6.

4,5 It will be observed that if the duration of. time between thermostatic demands for furnace -operation are relatively short the re in all probability will not go out and under these conditions during the time that element 6| is flexing in a A50 direction to bring contacts 62 and 63 together there Willbe a rise in stack temperature causing opening of switch 5| by reason of thel supply of fuel and ail` during the timing interval. Thus when contacts 62 and 63 are brought together 55 switch 5| will be open ard valve 21--will therefore not be opened. It is seen therefore that the igniting .unit -23 is only operated when upon a thermostatc demand for heat the fire has receded to such an extent that it will not recover of itself when fresh fuel is supplied. Opening of the mercury switch 56 or of the safety pilot 3| will of course preventqenergization of the relay by thermostat 35. From the foregoing, it is apparent that I have provided a combustion control system for solid fuel having improved means for igniting the fuel and controlling the igniting of the fuel whereby f personal attention to the apparatusis made entirely unnecessary. The apparatus is efficient and economical in that it only operates the gas igniting unit in the event lthat the fire has re- .ceded to such an extent that it will not recover when the fuel is added thereto. The controls provide for a predetermined interval of time before operating the igniting unit to see whether Switch will of course,

As soon as its'operation is necessary or not. If operation ofthe igniting unit is necessary, its operation is' immediately terminated when a rise in stack temperature indicates that there has been proper establishment of combustion. These results are 5 obtained 'in my system without using a calibrated combustion responsive switch and thus the difficulties inherent in the use of such devices are avoided.

While I have shownfan igniting unit comprising a gas burner, itis within the realm of my invention to use other forms of igniting devices. The single embodiment of my invention disclosed is a preferred representative form but other forms, modifications, and Vvariations'in the inven- 15 tion are Within my contemplation and the invention is to be limited only in accordance with the appended claims.

I claim as my invention:

1. In apparatus of the character described, in combination, means forming a combustion chamber adapted to contain a solid fuel, means associated With said combustion chamber constructed Iand arranged for igniting solidy fuel therein,

means for .feeding solid fuel to said combustion chamber, control means for said fuel feeding means and igniting means comprising a condition responsive control instrument, and means whereby said igiting means isv operated in response to said control instrument only in the absence of a temperature rise in said combustion chamber after starting of the fuel feeding means.

2. In apparatus of the character described, in combination, means forming a combustion chamber adapted to contain a solid fuel, means associated with lsaid combustion chamber constructed and arranged for igniting solid fuel therein. means for feeding solidl fuel to said combustion chamber, control means for said fuel feeding means and igniting means comprising a condition 40 responsive control instrument, timing means, and combustion responsive means, said timing means causing operation o f said igniting means after starting of the fuel feedingmeans in" the absence of the indication of a rise in temperature in said combustion chamber by said combustion responsive means.

3. In apparatus of the character described, in combination, means forming a combustion chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means 'for feeding solid fuel to said combustion chamber, control means for lsaid fuel feeding means and igniting means comprising a condition responsive control instrument, timing means, and combustion responsive means, said timing means starting a timing period upon a demand for combustion by said instrument, and said timing means causing said igniting means to operate at 0 the end of said period if said combustion respo sive means has not been actuated' ,by a rise in temperature. i

4, In apparatus of the character described, in combination, means forming a combustion chamberadapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for feeding solid fuel to said combustion chamber, control `means for said fuel feeding y means and igniting means comprising a 'condition responsive control instrument, timing means for causing operation of said igniting meansat a predetermined time after a demand for combustion by said instrument, and combustion responsive means for preventing operation 'of said igniting means at said predetermined time if combustion exists ln the combustion chamber.

5. In apparatus of the character described, in combination, means 'forming a combustion chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for feeding solid fuel to said combustion chamber, control means for said fuel feeding means and igniting means comprising a thermostat, a timer, and a switch responsive to a temperature increase'in the combustion space, said timer controlling said igniting means dependently on said switch and said switch preventing operation of the igniting means if a temperature rise occurred during the interval of said timer.

6. In a control system, in combination, a solid fuel red combustion device, a fuel igniting device, control means comprising a thermostat, a timer, and a switch responsive to an increase in temperature in the combustion space, said thermostat causing said timer to start a. timing pe- 1 riod upon a demand for combustion, said switch opening during said period if there is an increase in temperature in the combustion space, and said timer causing operation of said fuel igniting device at the end of said period if said switch is closed.

7. In apparatus of the character described, in combination, means forming a combustion chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for feeding solid fuel to said combustion chamber, and control means comprising a condition responsive control instrument controlling said fuel feeding means and igniting means whereby combustion can be initiated in said combustion chamber in response to said control means, said control means including means for causing operation of said igniting means depending upon whether or not there is an increase in combustion after starting of the fuel feeding means.

8. In apparatus of the character described, in combination, combustion means comprising a chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, control means for said combustion means comprising a condition responsive control instrument, and means whereby said igniting means is operated in response to said control instrument only in the absence of a temperature rise in said combustion chamber after a demand for combustion by said control instrument.

9. In apparatus of the character described, in combination, combustion means comprisingv a chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for supplying air for combustion of said fuel, control means for said air supplying means and igniting means comprising a condition responsive control instrument, said instrument being operable to cause air to be supplied by said air supplying means in response to a demand for combustion, and means whereby said igniting means is operated in responseto said control instrument only in the absence of a temperature rise in said combustion chamber after a demand for combustion by said instrument.

10. In apparatus of the character described, in combination, combustion means comprising a chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, control means for said combustion means comprising a condition responsive control instrument, and means whereby said igniting means is operated in response to said control instrument only in the absence of a temperature rise in said combustion chamber within a predetermined time after a demand for combustion by said control instrument.

11. In apparatus of, the character described, in combination, combustion means comprising a chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for supplying air for combustion of said fuel, control means for said air supplying means and igniting means comprising a condition responsive control instrument said instrument being operable to cause air to be supplied by said air supplying means in response to a demand for combustion, and means whereby said igniting means is operated in response to said control instrument only in the absence of a temperature rise in said combustion chamber Within a predetermined time after a demand for combustion by said instrument.

12. In apparatus of the character described, in combination, means forming a combustion chamber adapted to contain a solid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, means for feeding solid fuel to said combustion chamber, control means for said fuel feeding means and igniting means comprising a condition responsive control instrument, and means whereby said igniting means is operated in response to said control instrument only in the absence of a temperature rise in said combustion chamber Within a predetermined time after starting of the fuel feeding means.

i3. In apparatus of the character described, in combination, combustion means comprising a chamber adapted to contain a solid fuel, means associated `with said' combustion chamber constructed and arranged for igniting solid fuel therein, control means for said combustion means comprising a condition responsive control instrument, timing means, and means whereby said timing means causes operation of said igniting means after starting of the fuel feeding means in the absence of a rise in temperature in said combustion chamber.

14.-. In apparatus of the character described, in combination, combustion means comprising a chamber adapted to contain asolid fuel, means associated with said combustion chamber constructed and arranged for igniting solid fuel therein, control means for said combustion means comprising a condition responsive control instrument, timing means, and combustion responsive means, said timing means starting a timing period upon a demand for combustion by said instrument, and said timing means causing said igniting means to operate at the end of said period if said combustion responsive means has not been actuated by a rise in temperature.

FREDERICK E. LANGE. 

